1. Field of the Invention
This invention relates to a reproducing apparatus which excels in dubbing characteristics.
2. Description of the Prior Art
Still picture video recording systems (hereinafter will be called SV systems) are known which record still picture video signals on a magnetic disc or the like. The magnetic disc, which is employed as the information recording medium for the SV system, has, for example, a luminance signal recorded within a high zone and a color signal recorded within a low zone in a color-difference line sequence, as shown in FIG. 1 of the accompanying drawings, in a frequency spectrum either in the form of field recording covering just one field or in the form of frame recording covering two fields.
In a reproducing apparatus, therefore, the color signal must be interpolated to have line sequential color difference signals converted into concurrent color difference signals. Further, in the case of field recording, the signal must be converted into a frame signal for the purpose of having an interlace display at a monitor. For the conversion, interpolation is generally carried out by averaging horizontal line signals. This method is highly advantageous as it gives an improved resolution at the monitor.
In case of dubbing, however, the above-stated interpolating method degrades the resolution, because: in the format of a standard SV system, the line sequential color difference signals (B-Y and R-Y) are allowed to have an arbitrary phase in the odd- and even-number fields; further, in the case of field recording, the signal is allowed to be recorded in either an odd-number field or an even-number field. This shortcoming of the prior art is further described with reference to FIGS. 2A and 2B as follows:
In FIGS. 2A and 2B, the illustrations include 0.5 H delay (DL) circuits 1 and 4, with reference symbol H denoting a horizontal line period; switch circuits SW1 to SW4; and 1 H delay circuits 2, 5 and 6. These circuits are disposed within an output circuit of a reproducing apparatus which will be described later herein.
FIG. 2A shows a luminance (Y) signal interpolation circuit. The switches SW1 and SW2 are arranged to be switched over every field. Accordingly, the input Y signal is produced in a state of having been delayed by 1 H (horizontal period) for a first field. For a next field, the Y signal is skew compensated by the 0.5 H delay circuit 1 and is then averaged with the input and output signals of the next 1 H delay circuit 2 used. As a result, an interpolation signal which is delayed by 1.5 H is produced from the luminace (Y) signal interpolation circuit.
FIG. 2B shows a color (C) signal interpolation circuit. In this circuit, the switch SW3 and the 0.5 H delay circuit 4 are provided for the purpose of skew compensation. The 1 H delay circuits 5 and 6 and the switch SW4 are provided for changing the line sequential color difference signals into concurrent signals. More specifically, the incoming line sequential signals include R-Y and B-Y signals for every H period. Therefore, another color difference signal which does not include them is made into concurrent signals by averaging (interpolating) 0 H and 2 H signals. Therefore, the concurrent color difference signals become: EQU R-Y: 1 H, 1/2 (0 H+2 H), 1 H EQU B-Y: 1/2 (0 H+2 H), 1 H, 1/2 (0 H+2 H)
Thus, one of the color difference signals is always produced as an interpolated concurrent signal. Therefore, during the process of dubbing the luminance signal, the interpolated signal might be dubbed in reproducing the information which has been field recorded while, for the color signal, the interpolated color difference signal will be always dubbed. With the dubbing repeated, therefore, the vertical resolution degrades in proportion to the number of repeating times of dubbing. In the event of horizontal interpolation, the horizontal resolution is likewise degraded.
Further, in having information recorded on a magnetic disc dubbed to another disc, there arises the following problem of time base variations: A time base variation caused by a motor and a time base variation caused by variations in loads on the disc and a magnetic head result in a small picture distortion in the horizontal direction of a reproduced picture. At present, this is corrected by the AFC characteristic of the display. However, if the time base variations become excessive according as the dubbing is repeated, the correction becomes no longer possible.
Another problem of the prior art resides in that in the magnetic conversion system of the reproducing apparatus, the S/N ratio of a reproduced modulated signal is deteriorated by an AM noise resulting from a slight difference in touch between the magnetic disc and the magnetic head, a sliding noise, the thermal noise of the magnetic head, a modulation noise, etc.
It is a further problem of the prior art that there takes place deterioration of a high frequency characteristic mainly in the recording and reproducing system including the magnetic disc and the magnetic head.